Road Testing BMW’s Hydrogen 7

BMW produces its first street-legal car with a hydrogen-powered combustion engine. The automaker says it will put 100 of the Hydrogen 7 cars in circulation next year in the United States, Europe and Asia.

BERLIN — Jules Verne, in his 1874 novel The Mysterious Island, described hydrogen as an "inexhaustible source of heat and light." A little over 130 years later, BMW is testing the theory with an innovative internal combustion engine that burns the lightest element much like gasoline, only cleaner.

Wired News was invited to test-drive one of BMW's new Hydrogen 7 automobiles recently. It proved a serious step forward in using hydrogen as a potential energy source for cars, while showing defects that make the concept a clear work in progress.

BMW is the only major carmaker to bring a car with a hydrogen-combustion engine beyond the prototype stage.

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The automaker's approach is markedly different than the more familiar concept of hydrogen-powered fuel cells, where energy is stored before it is converted into electricity. By contrast, BMW's Hydrogen 7 is powered by pumping hydrogen into a combustion engine and igniting it. The engine can burn both hydrogen and gasoline, and switches between the two at the flick of a switch.

Burning hydrogen is more efficient than converting it into electricity, making it the more practical choice for hydrogen-fueled cars now, according to BMW.

The automaker is taking that premise to the road with a limited test release next year. BMW said it will put 100 of the hydrogen models into circulation in the United States, Europe and Asia. The cars will be loaned to high-profile people, BMW says, such as celebrities and politicians. If the cars become sufficiently popular, BMW says it can go into full-scale production, without commenting how much the model will cost.

The test drive confirmed the vehicles are road-ready. But some major issues need to be worked out, particularly with acquiring and storing the liquid hydrogen fuel.

At 110 mph along the highway on the outskirts of Berlin the sedan handles much like the German luxury carmaker's flagship BMW 7 Series model, on which it is based. In total, the liquid hydrogen tank, heat exchangers and other components add an extra 550 pounds to the car's weight — and you feel the extra load. However, performance was not drastically different than the 7 Series BMW.

When pushed, the 12-cylinder, 260-horsepower engine emits a high-pitched whine like that of the diesel version of the 7 Series. It is not exactly a speed demon, but it doesn't lack power; after pulling onto an exit ramp, I accelerated from zero to 62.5 mph with two adult passengers in less than 10 seconds.

The car switches from hydrogen to gas mode with the press of a button on the steering wheel. I heard a small click from behind the backseat without any change in my speed or acceleration along the highway.

BMW's first hydrogen-powered car has a lot to be excited about. The byproduct of the engine's combustion process is almost exclusively water vapor, which comes out of an exhaust pipe. However, some nitrous oxide and carbon dioxide are emitted, so the Hydrogen 7 is not a zero-emission car.

CO2 emissions are 1 percent of the maximum emission levels in the United States and Europe, while N2O levels are 30 percent and 2 percent of the maximum levels in those same regions, respectively, BMW says. A planned hydrogen-only model will further reduce N2O emissions to within 10 percent of the maximum levels in the United States, BMW says.

One major challenge is how to keep the hydrogen cooled to minus 253 degrees Celsius (minus 423 degrees Fahrenheit) so it remains in liquid form without boiling off. Despite the double-walled, stainless-steel tank that stores the liquid in high-vacuum conditions with aluminum reflective foil, the liquid hydrogen in the 8-kilogram fuel tank begins to boil after 17 hours if the car remains parked. The tank empties completely after 10 to 12 days.

During the test drive, I pulled over to a Total hydrogen filling station to tank up.

The BMW Hydrogen 7 holds approximately 8 kilograms of liquid hydrogen. The car consumes about 15 miles per kilogram for a total cruising range of 120 miles, BMW says. In gas mode, the car's 74-liter (19.5-gallon) gasoline tank offers a range of about 300 miles.

At $10.30 per kilogram, hydrogen fuel is no bargain, even in Europe, where gas prices are significantly higher than in the United States. Filling up a 74-liter gas tank in Germany with high-test gas costs about $123, which for a cruising range of 300 miles is a much better deal than $82.40 you'll pay to go 120 miles on hydrogen fuel. The price of hydrogen is astronomical compared to the $2.20 or so per gallon price in the United States. However, BMW representatives on hand for the car demonstration in Berlin last week said hydrogen pump prices should be significantly lower if production increases for use as car fuel.

Hydrogen's high flammability, compared to other fuel mixes, raises concern for many (especially for me while standing next to the fuel pumps). The Hindenburg and the Challenger both ran on hydrogen, although the fuel mix was not what triggered those disasters. According to BMW, the risks posed by hydrogen are at the very worst comparable to those of gas. At the fueling station, sensors will shut down fuel flow from the pumps if a leak is detected, while the car's engine and hydrogen gas flow will also stop in case of a puncture or leak, BMW says.

Hydrogen is primarily produced from natural gas, a process that generates more CO2 than gasoline car engines. However, solar, wind and hydroelectric generation of hydrogen and its extraction from biomass represent viable long-term options that promise negligible CO2 emission, BMW says.

The automaker concedes its Hydrogen 7 production car is just a start. The model's acceleration and mileage pale in comparison with many ethanol-fueled and gas-electric-hybrid models, such as the latest Lexus hybrid. Company engineers are working to introduce lower pressure in the fuel tank to limit how fast the liquid hydrogen boils off. And they're researching new materials for a lighter and less bulky fuel tank.

The dearth of fueling stations will hamper drivers who need to fill up in the middle of places like Kansas. For the 100 Hydrogen 7s in operation next year, BMW says hydrogen filling stations will be located in the vicinity of where the cars are loaned, albeit probably fewer than 12 worldwide in 2007. Hydrogen trucks will offer mobile fill-ups for the loaned cars, BMW says.

Ultimately, BMW engineers hope to develop an engine that offers acceleration and power comparable to any gasoline internal-combustion engine vehicle. To do that, BMW says it is developing a hydrogen-only internal-combustion engine that will produce 95 kilowatts of power per liter instead of the 32 kilowatts per liter now in the Hydrogen 7, with direct, cryogenic injection in a pure hydrogen tank. On a per-volume basis, cryogenic liquid hydrogen offers 75 percent more energy compared to hydrogen in a compressed gaseous state at 700 bars of pressure, BMW says.

"This will take some time," said Frank Ochmann, head of the Hydrogen 7 project. "We will have (this capability), but the question is when we make the decision to do it."

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